1. Field of the Invention
The present general inventive concept relates to a hard disk drive, and more particularly, to a hard disk drive which can prevent a defect such as a rapid off track phenomenon caused by different thermal expansions between a voice coil motor (VCM) and a base, being manufactured of different materials.
2. Description of the Related Art
Hard disk drives (HDDs) which record and reproduce data with respect to a disk using a read/write head are widely used as auxiliary memory devices in computer systems because of their fast access time to a large amount of data. With the recent increase in TPI (track per inch; a density in a direction along the rotation of a disk) and BPI (bits per inch; a density in a direction along the thickness of a disk), the HDD has achieved a significant increase in its capacity and its application field has expanded greatly. Accordingly, there has been an increasing demand for the development of compact HDDs which can be used for portable electronic products such as notebooks, personal digital assistants (PDAs), and mobile phones. Actually, a compact HDD having a diameter of 0.85 inches, which is similar to the size of a coin, has been recently developed and is expected to be used for mobile phones in the future.
The HDD includes a disk for recording data, a spindle motor for rotating the disk, a head stack assembly (HSA) having a read/write head to record and reproduce data with respect to the disk, a voice coil motor (VCM) for pivoting the HSA, and a base on which these elements are installed. The HSA pivots around a pivot shaft by the VCM and includes an actuator arm coupled to the pivot shaft capable of pivoting, a slider on which the read/write head is mounted, and a suspension installed on the actuator arm and supporting the slider to be elastically biased toward the surface of the disk. The slider is generally supported by the suspension while being attached to a flexure.
During a data recording and reproducing process, a lift force generated by the rotation of the disk and an elastic force caused by the suspension operate on the slider having the head. Accordingly, the slider maintains an elevated state above a data zone of the disk at a height at which the lift force and the elastic force are balanced. Therefore, the read/write head mounted on the slider records and reproduces data with respect to the disk while maintaining a predetermined displacement from the disk.
The HDD records and reproduces the data in response to a command from a host system. In the HDD, it is preferable that the data is accurately recorded along the center of a track. However, a typical read/write head may drift to the left and right along the center of the track due to the response characteristic of a tracking control circuit and bias applied to the read/write head. A degree of the deviation of the read/write head from the center of track, that is, off-track, can be detected by a servo burst signal recorded in a servo sector area. A signal indicating the size of the off-track is typically referred to a position error signal (PES).
When the off-track is considerable, the data recorded on neighboring tracks may be deleted by the recording for a target track. Although the reduction of the PES gradually becomes difficult according to the increase of TPI due to the high density of the HDD, a variety of methods are presently developed to reduce an off-track error.
Separately from the off-track phenomenon, a rapid off track (ROP) phenomenon may occur such that the read/write head following a track momentarily deviates from a current track due to an external effect. The ROP phenomenon rapidly drops the accuracy in a targeted track and may cause a defect to the HDD or reduce the reliability of the HDD.
The ROP phenomenon is presently believed to occur as a VCM yoke and the base are made of different materials which are known to exhibit a degree of different thermal expansion during a temperature change. In detail, the VCM yoke of the VCM and the HSA are directly coupled to the base. In general, the VCM yoke is made of a stainless steel and the base is made of aluminum. Thus, when a surface temperature increases during the operation of the HDD, the VCM yoke and the base exhibit different thermal expansion due to different thermal expansion coefficients. As the different thermal expansion becomes excessive, the ROP phenomenon occurs so that the read/write head momentarily deviates from the desired track.
When the HDD is driven by applying electric power, the surface temperature of the HDD increases as time passes so that parts of the HDD thermally expand. During the thermal expansion, deformation due to the different thermal expansion can be prevented to a certain degree by increasing the torque of a screw coupling the VCM yoke and base. However, when the thermal expansion is beyond the limit of the torque, deformations (such as from an earthquake) can cause the ROP phenomenon to occur, in which the read/write head momentarily deviates from the desired track.
To overcome the above problem, a method of fixing the VCM yoke to one side of the base only and allowing the other side to freely expand has been introduced. Nevertheless, this method has not sufficiently reduced the ROP phenomenon that is generated from the different thermal expansion caused by the different thermal expansion coefficients in the high capacity HDD.